1. Field of the Invention
The present invention relates to a communication device and a method used in a wireless communication system, and more particularly, to a communication device and a method of handling a hybrid automatic repeat request process in a licensed assisted access secondary cell.
2. Description of the Prior Art
A long-term evolution (LTE) system provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes at least one evolved Node-B (eNB) for communicating with at least one user equipment (UE), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, increases peak data rate and throughput, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), licensed-assisted access (LAA) using LTE, etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3rd Generation Partnership Project (3GPP) Rel-10 standard or later versions.
The eNB may communicate with the UE in an unlicensed band via the LAA using LTE technique. The eNB may schedule the UE to transmit data in a subframe in the unlicensed band. However, the UE may not complete the transmission of the data to the eNB in the subframe due to a status (e.g., channel is busy) of the unlicensed band. According to the prior art, it is unknown whether the UE continues to monitor the unlicensed band, if the UE does not complete the transmission of the data.
Thus, how to handle a communication operation between the eNB and the UE in the unlicensed band is a problem to be solved.